Hint: The blue and green squares form a Type 3 Discontinuous Nice Loop ([R4C2] -3- [R1C2] =3= [R2C1] -3- [R9C1] -7- [R7C2] =7= [R4C2]). The discontinuity is at the blue square. Candidate 3 can be eliminated from this square.

My 1st of many questions is the notation ([R4C2] -3- [R1C2] means a weak link between ([R4C2] & [R1C2] which are candidates [379] vs [38] is this true?

2nd-Is this a weak link because these two cells ([R4C2] & [R1C2] share only one candidate=3 ??

3rd-Isn't there also a link between ([R4C2] & [R7C2] which are candidates [139] vs [1379] ?

I understand xy chains,forcing chains and forcing loops since these only include bivalue cells. However I am totally confused when cells with 3 or more candidates are in the equation.

Can someone explain the notation as to why there are weak links and strong links.([R4C2] -3- [R1C2] =3= [R2C1] -3- [R9C1] -7- [R7C2] =7= [R4C2]). The discontinuity is at the blue square. Candidate 3 can be eliminated from this square.